Figure 13-2 A Cepheid Variable Star in Galaxy M100 One of the most reliable ways to determine the distance to moderately remote galaxies is to locate Cepheid variable stars in them, as discussed in the text. The distance of 50 million ly (15.2 Mpc) from Earth to the galaxy M100 in the constellation Coma Berenices was determined using Cepheids. Insets: The Cepheid in this view, one of 20 located to date in M100, is shown at different stages in its brightness cycle, which recurs over several weeks.